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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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package com.sun.xml.internal.bind.api;

import javax.xml.bind.JAXBContext;

import javax.xml.bind.Unmarshaller;

import javax.xml.bind.ValidationEventHandler;

import javax.xml.bind.annotation.XmlAnyElement;

import com.sun.istack.internal.NotNull;

import com.sun.istack.internal.Nullable;

/**

 * Dynamically locates classes to represent elements discovered during the unmarshalling.

 *

 * <p>

 * <b>THIS INTERFACE IS SUBJECT TO CHANGE WITHOUT NOTICE.</b>

 *

 * <h2>Background</h2>

 * <p>

 * {@link JAXBContext#newInstance(Class...)} requires that application informs JAXB

 * about all the classes that it may see in the instance document. While this allows

 * JAXB to take time to optimize the unmarshalling, it is sometimes inconvenient

 * for applications.

 *

 * <p>

 * This is where {@link ClassResolver} comes to resucue.

 *

 * <p>

 * A {@link ClassResolver} instance can be specified on {@link Unmarshaller} via

 * {@link Unmarshaller#setProperty(String, Object)} as follows:

 *

 * <pre>

 * unmarshaller.setProperty( ClassResolver.class.getName(), new MyClassResolverImpl() );

 * </pre>

 *

 * <p>

 * When an {@link Unmarshaller} encounters (i) an unknown root element or (ii) unknown

 * elements where unmarshaller is trying to unmarshal into {@link XmlAnyElement} with

 * <tt>lax=true</tt>, unmarshaller calls {@link #resolveElementName(String, String)}

 * method to see if the application may be able to supply a class that corresponds

 * to that class.

 *

 * <p>

 * When a {@link Class} is returned, a new {@link JAXBContext} is created with

 * all the classes known to it so far, plus a new class returned. This operation

 * may fail (for example because of some conflicting annotations.) This failure

 * is handled just like {@link Exception}s thrown from

 * {@link ClassResolver#resolveElementName(String, String)}.

 *

 * @author Kohsuke Kawaguchi

 * @since 2.1

 */

public abstract class ClassResolver {

    /**

     * JAXB calls this method when it sees an unknown element.

     *

     * <p>

     * See the class javadoc for details.

     *

     * @param nsUri

     *      Namespace URI of the unknown element. Can be empty but never null.

     * @param localName

     *      Local name of the unknown element. Never be empty nor null.

     *

     * @return

     *      If a non-null class is returned, it will be used to unmarshal this element.

     *      If null is returned, the resolution is assumed to be failed, and

     *      the unmarshaller will behave as if there was no {@link ClassResolver}

     *      to begin with (that is, to report it to {@link ValidationEventHandler},

     *      then move on.)

     *

     * @throws Exception

     *      Throwing any {@link RuntimeException} causes the unmarshaller to stop

     *      immediately. The exception will be propagated up the call stack.

     *      Throwing any other checked {@link Exception} results in the error

     *      reproted to {@link ValidationEventHandler} (just like any other error

     *      during the unmarshalling.)

     */

    public abstract @Nullable Class<?> resolveElementName(@NotNull String nsUri, @NotNull String localName) throws Exception;

}